[flang] Diagnose bad attributes of implicit interface externals

Procedures with the EXTERNAL attribute (explicit or implied) are
not permitted to be ALLOCATABLE or be arrays if their interfaces
are implicit.

Differential Revision: https://reviews.llvm.org/D146572

Author: klausler

flang/lib/Semantics/check-declarations.cpp

@@ -426,6 +426,17 @@ void CheckHelper::Check(const Symbol &symbol) {
         " of a module"_err_en_US,
         symbol.name());
   }
+  if (IsProcedure(symbol) && !symbol.HasExplicitInterface()) {
+    if (IsAllocatable(symbol)) {
+      messages_.Say(
+          "Procedure '%s' may not be ALLOCATABLE without an explicit interface"_err_en_US,
+          symbol.name());
+    } else if (symbol.Rank() > 0) {
+      messages_.Say(
+          "Procedure '%s' may not be an array without an explicit interface"_err_en_US,
+          symbol.name());
+    }
+  }
 }
 
 void CheckHelper::CheckCommonBlock(const Symbol &symbol) {
@@ -916,7 +927,7 @@ void CheckHelper::CheckProcEntity(
     }
     CheckPassArg(symbol, details.procInterface(), details);
   }
-  if (symbol.attrs().test(Attr::POINTER)) {
+  if (IsPointer(symbol)) {
     CheckPointerInitialization(symbol);
     if (const Symbol * interface{details.procInterface()}) {
       const Symbol &ultimate{interface->GetUltimate()};
@@ -936,7 +947,7 @@ void CheckHelper::CheckProcEntity(
             symbol.name()); // C1517
       }
     }
-  } else if (symbol.attrs().test(Attr::SAVE)) {
+  } else if (IsSave(symbol)) {
     messages_.Say(
         "Procedure '%s' with SAVE attribute must also have POINTER attribute"_err_en_US,
         symbol.name());

flang/test/Semantics/call05.f90

@@ -121,7 +121,9 @@ subroutine test
 
 module m2
 
+  !ERROR: Procedure 't3' may not be ALLOCATABLE without an explicit interface
   character(len=10), allocatable :: t1, t2, t3, t4
+  !ERROR: Procedure 't6' may not be ALLOCATABLE without an explicit interface
   character(len=:), allocatable :: t5, t6, t7, t8(:)
 
   character(len=10), pointer :: p1

flang/test/Semantics/resolve20.f90

@@ -21,6 +21,7 @@ subroutine foo2
   procedure(h) :: i
   procedure(forward) :: j
   !ERROR: 'bad1' must be an abstract interface or a procedure with an explicit interface
+  !ERROR: Procedure 'k1' may not be an array without an explicit interface
   procedure(bad1) :: k1
   !ERROR: 'bad2' must be an abstract interface or a procedure with an explicit interface
   procedure(bad2) :: k2